RENO, Nev. (AP)  With the start of summer two months away, the Truckee River’s level already is dropping around Reno after flows into it from a Sierra Nevada reservoir were halted last week.

Federal Water Master Chad Blanchard said he needed to begin closing Boca Reservoir’s floodgates on Thursday because of its low water levels stemming from the four-year drought.

“We’re out of water and we’re ramping it down,” he told the Reno Gazette-Journal (http://on.rgj.com/1JkAiuQ ). “It’s something we’ve never seen before. We’ve never run out this early before.”

It’s the earliest the flow has been cut off since record keeping began more than a century ago, he said. The previous earliest date was June 5, 1992, during the height of another drought. Last year, the flow from Boca was cut off July 31.

“It’s way beyond what we imagined we would see,” Blanchard said. “We’re in uncharted waters, or uncharted lack of waters.”

The Sierra snowpack has been well below average the last four winters, with the most recent one the worst yet. The Truckee River basin’s snowpack on Thursday was 15 percent of average for the date. The Lake Tahoe basin’s snowpack was even worse: zero.

Tahoe dropped below its natural rim in October, cutting off its flow into the Truckee. Tahoe is not expected to rise above its natural rim this year. The Truckee flows more than 100 miles from Tahoe to Pyramid Lake, about 30 miles north of Reno.

Boca Reservoir impounds waters of the Little Truckee River, a major tributary of the Truckee. The reservoir is located in the Tahoe National Forest near Truckee, California.

With the flow out of Boca halted, river levels will quickly drop and the Truckee will be fed mostly by scant natural snowmelt from its other tributaries.

The Truckee’s summer flows now will only come from reservoir storage dedicated to the Pyramid Lake Paiute tribe to maintain its fisheries and to the Truckee Meadows Water Authority to provide water for the Reno area.

The authority has asked its customers to cut water use by at least 10 percent.